Why are tomatoes really fruit but we think of them as vegetables? In 1893, the Supreme Court ruled that the tomato must be considered a vegetable, even though, botanically, it is a fruit.
Because vegetables and fruits were subject to different import duties, it was necessary to define it as one or the other. A tomato was declared to be a vegetable because they were commonly eaten as one.
To really figure out if a tomato is a fruit or vegetable, you need to know what makes a fruit a fruit, and a vegetable a vegetable. The big question to ask is, does it have seeds? If the answer is yes, then technically, you have a fruit. Generally, a fleshy growth originating from a flower and carry seeds is considered a fruit. So gourds, cucumbers, pea pods, squash, green beans and walnuts are fruit too.
A potato fails because it does not come from the flower and is part of the root. Vegetables such as, radishes, celery, carrots, and lettuce do not have seeds (that are part of what we eat) so they are grouped as vegetables.
Certain fruits like tomatoes and green beans will probably always be referred to as "vegetables" in today's society.